Method for producing cast ferrous alloy



June 5, 1956 K. D. MlLLlS El AL METHOD FOR PRODUCING CAST FERROUS ALLOYFiled Sept. l0 1949 2 Sheets-Sheet l June 5, 1956 K. D. MlLLls ETAL2,749,238

METHOD Foa PRoDUcING CAST FERROUS ALLOY Filed Sept. lO, 1949 2Sheets-Sheet 2 BY m ATTORNEY METHOD FR PRODUCING CAST FERROUS ALLOYKeith Dwight Millis, Rahway, Albert Paul Gagnebin, Red

Bank, and Norman Boden Pilling, Westfield, N. E., assignors to TheInternational Nickel Company, Inc., New York, N. Y., a corporation ofBelaware Application September 10, 1949, Serial No. 115,088

23 Claims. (Cl. 75-130) The present invention relates to a method forproducing a unique ferrous alloy possessing advantageous features ofgray cast iron and malleable iron, but devoid of defects andshortcomings thereof, and, more particularly, to a method for producinga new ferrous product having improved and unusual combinations ofproperties, especially an improved and unusual combination of foundingproperties and mechanical and physical properties.

Cast iron is a eutectiferous alloy comprised mainly of iron andcontaining carbon, and usually a substantial amount of silicon, thecarbon being present in excess of the amount which can go into solidsolution in austenite at the eutectic temperature of the alloy, whereassteel is an alloy which contains less than this amount of carbon andwhich does not exhibit a eutectic of iron and carbon. Cast irons areusually considered as being either white cast iron or gray cast iron.Sometimes a cast iron which possesses some of the characteristics orstructural features of a White cast iron and some of the characteristicsor structural features of a gray cast iron is termed a mottled castiron, but for general purposes and for purposes of the presentdescription, such a product is classified as either a white cast iron ora gray cast iron, depending upon which characteristics or structuralfeatures predominate. The kind of cast iron which has generally beenmost commonly used for centuries is gray cast iron, i. e., the soft andmachinable kind in which the major part of the carbon not required toforni the matrix structure is present as graphite in the as-castcondition. It has been recognized that the graphitic carbon occurs aselongated particles, commonly called flake graphite, disseminatedthroughout the matrix. ln polished gray cast iron sections, the flakegraphite appears under the microscope as a grayish, soft constituent.The weakening discontinuities produced by flake graphite are reflectedin the greatly reduced tensile strength, fatigue resistance, toughnessand ductility of gray cost iron compared to a product made up entirelyof the matrix cornponent, e. g., a comparable steel. White cast iron isa harder, brittle cast iron in which the major part of the excess carbonnot required to form the matrix is present as combined carbon, i. e., ascarbide, in the as-cast condition. While some advances, considerednotable at the time, have been made in ordinary foundry gray cast iron,no one has proposed prior to the present invention a satisfactory,generally applicable method for eliminating from ordinary foundry graycast iron the detrimental effect of graphite due to its ake form in theas-cast condition. As a result, it has been necessary to resort to theuse of ferritic or pearlitic malleable iron or even cast steel whenhigher properties or combinations of properties were required, althoughthese engineering materials are considerably more expensive than graycast iron and possess other disadvantages.

The present invention is based on the discovery of a method wherebycarbon in a high-carbon as-cast ferrous alloy, i. e., in an as-castferrous alloy containing carbon within the cast iron range, can be madeto appear aired States Patent 2,749,238 Patented June 5, 1956consistently and reproducibly in the form of dispersed gray-colored,soft particles substantially spheroidal or spherical in shape andgenerally having a radial structure, thereby eliminating the deleteriouseffects of ilake graphite. In the ferrous alloy produced by the methodembodying the present invention, this form of carbon can be obtained inthe as-cast condition, i. e., without heat treatment, together with acombination of properties of an order entirely different from and higherthan that obtained in gray cast iron.

It is among the objects of the present invention to provide methods orprocesses for consistently and reproducibly eliminating ake graphitesubstantially or entirely from high-carbon ferrous alloys, and toprovide highcarbon as-cast ferrous alloys in which carbon occurs assubstantially spheroidal or spherical, soft, gray-colored particles.

Other objects and advantages of the present invention will be apparentto those skilled in the art from the following description taken inconjunction with the drawings in which:

Figs. l and 2 are reproductions of photomicrographs taken at amagnification of 25 diameters and showing, in polished sections ofrepresentative alloys produced by the process contemplated by thepresent invention, the spheroidal form of carbon obtained inthe as-castcondition by the presence of a special element employed in the processcontemplated by the present invention;

Fig. 3 is a reproduction of a photomicrograph taken at a magnificationof 250 diameters and showing the etched structure in the as-castcondition of an alloy produced in accordance with the present inventionand containing the spheroidal form of carbon in a pearlitic matrix;

Fig. 4 is a reproduction of a photomicrograph taken at 50 diametersshowing the occurrence of the spheroidal form of carbon in the etchedstructure of an alloy in the as-cast condition and produced inaccordance with the invention;

Fig. 5 is a reproduction of a photomicrograph taken at a magnificationof 1000 diameters of an etched specimen and showing in more detail thestructure of the spheroidal form of carbon obtained in alloys in theascast condition produced by the process contemplated by the presentinvention;

Fig. 6 is a reproduction of a photomicrograph taken at a magnication of1000 diameters on an etched specimen and showing in detail the structureof the spheroidal form of carbon obtained in alloys produced by theprocess contemplated by the present invention after having been given atreatment to ferritize the matrix;

Fig. 7 is a reproduction of a photomicrograph taken at a magnificationof 250 diameters and showing the etched structure of a high-carbonferrous alloy containing a special element employed in the processcontemplated by the invention after a treatment to ferritize the matrix;and

Fig. 8 is a reproduction of a photograph of three bend-test specimensmade of the alloy produced by the process contemplated by the presentinvention, one specimen having been tested in the as-cast condition andthe other two specimens having been tested after different ferritizingtreatments.

The present invention provides a novel method for producing a novelferrous product containing at least about 50% iron and particularly atleast about 87% iron, carbon and silicon within the cast iron range, thecarbon in excess of that required to form the matrix being predominantlyin the uncombined form, and containing a small but effective amount ofmagnesium to control the form of uncombined carbon. The inventionprovides a cast iron product characterized by a microstructurecontaining carbon in the form of randomly dispersed, soft, gray-colored,substantially spheroidal or spherical particles or agglomerates of suchparticles. In accordance with the present invention, the aforementionedmicrostructure of the product is obtained in the as-cast condition toprovide a novel product characterized by an improved combination ofproperties and by a structure not reproducibly obtained prior to thepresent invention in cast irons in the as-cast condition. The product ofthe invention is preferably substantially devoid of flake graphite.Another distinguishing feature of the microstructure is that usually nosulfide particles are seen embedded in the matrix, whereas ordinary castiron usually contains many easily recognized sulfide inclusions embeddedin the matrix.

Generally speaking, the present invention contemplates the method forthe production of a new cast ferrous alloy containing uncombined carbonin a spheroidal form in the as-cast condition which comprisesestablishing a molten ferrous alloy bath of such composition that ifcast after inoculation it would be a gray cast iron, for example, ifcast in a sand mold or in the type of mold to be employed in producingthe final product shortly after a late inoculating addition such asconventionally employed in treating cast iron, incorporating magnesiuminto said bath in such amounts that a small but effective retainedmagnesium content (for example, about 0.035% or about 0.04% or moremagnesium) up to about 0.4% or 0.5% is obtained to produce thespheroidal carbon form in the final castings and inoculating the bath atleast once (preferably with a late addition of at least 0.2%, or morepreferably at least 0.3%, of silicon as a silicon-containing metallicagent such as ferro-silicon), and casting the inoculated bath. Usuallyabout 0.04% to about 0.4% magnesium, preferably at least about 0.05% toabout 0.2% or about 0.06% to about 0.15% magnesium is retained in thebath and in the castings produced therefrom when using ordinary foundryirons. It is preferred that inoculation be employed in carrying out theprocess embodying the present invention. However, in some cases, wherethe graphitizing power of the magnesium-containing bath is very high,inoculation may not be necessary to insure that a sutiicient amount ofthe total carbon will be in the uncombined form in the soliditiedcasting, although it has been found that inoculation is alwaysbeneficial. The instances where inoculation would not be necessary arerelatively exceptional. As those skilled in the foundry art know, theinoculation of ordinary cast iron has a graphitizing eiect and comprisesa late addition of a strong graphitizer which is usually asilicon-containing agent such as ferro-silicon, calcium silicide, nickelsilicide, etc., but may also be another strong graphitizer such asaluminum. By employing an agent containing both magnesium and theinoculating element, for example, a nickel-magnesium-silicon alloycontaining about 30% or 50% or more silicon, it is possible to introducethe magnesium and the inoculant by means of a single addition agent andsuch practice is within the scope of the present invention but is not aspreferred as inoculating after the magnesium introduction, as the latterprocedure generally is more effective in assuring the presence of thesoft, gray-colored spheroids or spheres with the required retainedmagnesium content in the as-cast product and produces higher properties.As indicated hereinbefore, the molten bath which is treated inaccordance with the invention is one which would be a gray cast iron ifcast after a graphitizing inoculation, e. g., in a sand mold or in thetype of mold to be employed to produce the tinal product. Of course, amolten bath with suicient graphitizing power to produce a gray cast ironWithout inoculation is within the scope of those that can be treated inaccordance with the present invention because such a bath obviouslylwould still be a gray cast iron if cast after inoculation which merelyfurther increases or insures graphitization in cast iron.

Under the microscope, the difference between the ascast product providedby the method embodying the present invention and gray cast iron isreadily apparent. In polished sections of the as-cast novel productprovided by the present invention, som-c or practically all of thespheroidal form of uncombined carbon appears as compact, soft,gray-colored, rounded particles, usually nearly circular. or asagglomerates or groups of such particles. The occurrence of thespheroidal form of carbon in polished (unetched) specimens of themagnesium-containing ferrous alloy in the as-cast condition isillustrated in Figs. l and 2. rfhe appearance of the spheroidal form ofcarbon in etched sections of the alloy in the as-cast conditionillustrated in Fig. 3 wherein the spheroidal carbon occurs in a matrixof pearlite. When the composition is such that the matrix containsferrite as well as pcarlite in the as-cast condition, the ferrite oftentends occur around the spheroidal carbon particles, as illustrated inFig. 4. in the tis-polished condition and particularly in the etchedcondition, the rounded particles of carbon seen in properly polishedsections generally have a well-defined radiating structure. Fig. 5 showsthe representative radiating or radial structure of the spheroidal orrounded particles which at a magnification of i000 diameters usually areabout l to 21/2 inches in average diameter in cast sections of normalthicknesses. in polished sections of gray cast irons, the uncombinedcarbon has appeared entirely or almost entirely as elongated particlesor iiakes which are very long in comparison to their Width. Thespheroidal or rounded particle seen under the microscope in polishedsections of thc magnesium-containing alloy generally has the appearanceof a plurality of crystals radiating from approximately the center, i.e., a radiating and polycrystalline appearance. When viewed underreflected polarized light through a microscope, radiating portions orsectors of the rounded particle (which apparently produce the radiatingor radial structure of the particle) extinguish at diiferent intervalsas the stage of the microscope is revolved. In gray cast ironscontaining iiake graphite, the entire flake, which has been recognizedto be a single crystal, usually extinguishes at one time during thestage rotation.

Retention of magnesium A feature of the present invention in obtainingthe aforementioned product having a microstructure containing thespheroidal form of carbon is the introduction of magnesium into themolten bath and the retention of at least a critical minimum amount ofmagnesium in the nal product. It is not suicient merely to add magnesiumto the molten bath. The presence of retained magnesium in the bath andin the aforementioned product is essential in order to obtain thespheroidal carbon structure therein. While the theory of the magnesiumeffect on the form of carbon and on the properties of the productprovided by the present invention is not fully apparent, it has beenfound that the presence of retained magnesium 1s required in order toobtain the compacted spheroidal or spherical, soft, gray-colored form ofcarbon and to obtain the high combination of properties in the as-castferrous alloy of the present invention. if the final product contains noretained magnesium or too small an amount of retained magnesium, theresults of the present invention as indicated by either the propertiesor thc carbon form are not obtained. As pointed out in the aforesaid U.S. Patent No. 2,485,760, it was recognized that magnesium determinationsof the order involved herein were difficult to make, and the valuesgiven herein are based upon analyses by a chemical wet method and Werereproducible within about 0.005% or so. It was also pointed out in theaforesaid patent that the accuracy of the values of retained magnesiumwere complicated by the presence of other elements associated with`magnesium in the ferrous product. A striking characteristic which isusually exhibited by the product produced by the process contemplated bythe invention, particularly in its preferred embodiment containing amajor proportion of the uncombined carbon in the spheroidal form, is theSteely appearance of its fracture as compared to the gray fracture ofgray cast iron. The minimum retained magnesium content, at which thespheroidal form of uncombined carbon is induced, generally increasesslightly with the carbon content and/or silicon content of the alloy andwith the section size of the casting to be produced. Thus, when aparticular treated bath is to be cast in a large section, e. g., fourinches, the retained magnesium content should be slightly increased ascompared to the satisfactory minimum retained magnesium content thatcould be employed if the same treated bath were to be cast in a smallsection, e. g.,

yone inch.

If any undesirable elements which tend to combine with and/or counteractthe effect of magnesium, for example, sulfur, etc. (including oxygen, ifany be present in the molten cast iron bath as is believed possible bysome metallurgists), are present in the bath or are subsequently added,the amount of magnesium introduced should be increased by the amountrequired to counteract the effect of the presence of these elements orimpurities by removing the elements or by otherwise overcoming theireffects. Obviously, if any undesirable elements are not present or arepresent in smaller amounts than usual, the amount of magnesiumintroduced could be decreased.. Sulfur is the magnesium-counteractingelement which is most likely to be present. No other common elements inthe usual amounts which occur in cast iron, with the possible exceptionof large amounts of copper, have been found to have any markeddetrimental eifect in interfering with the desired function ofmagnesium. Certain subversive elements which are comparatively rare incast iron and which should be avoided are discussed hereinafter. Whensulfur is present in the molten bath before treatment, it is necessaryto introduce into the bath an amount of magnesium which is suiiicientnot only to produce the desired retained magnesium content but also toreact with sulfur. In addition, the magnesium recovery under theparticular conditions and with the particular addition agents employedmust also be taken into consideration in determining the amount ofmagnesium to be added, as will be discussed in more detail hereinafter.It has been found that in all baths treated in accordance with thepresent invention, all the magnesium-containing agents which producedthe spheroidal form of uncombined carbon obtained by the invention alsointroduced the magnesium in a form which combined with sulfur present inthe bath with the result that the sulfur content was reduced to about0.010% to 0.015%, e. g., 0.012%. The results also have clearly indicatedthat only the unconsumed excess of magnesium is then available toperform its function of controlling the form of the uncombined carbonand providing the required retained magnesium content. Since many bathsthat can be treated in accordance with the invention will usuallycontain sulfur in various amounts as high as even 0.3% or more, it istherefore necessary to add an amount of magnesium which is sufficient tointroduce magnesium to combine with the sulfur and to provide an excesssuficient to give the retained magnesium content required by theinvention. In other words, the lower the content of sulfur, etc., thelower the amount of magnesium that need be introduced and retained. Theintroduction of about three parts by weight of magnesium is required toreact with about four parts by weight of sulfur. In actual practice, itis preferred to introduce one part by weight of magnesium for each partby weight of sulfur to be removed. Thus, if the bath contains 0.155%sulfur and it is desired to obtain a retained magnesium content of0.06%, then, since the sulfur content must first be re duced from 0.155%to about 0.015 about 0.14% mag nesium is introduced for this purpose andan additional 0.06% magnesium must be introduced to provide the desiredretained magnesium content. A total of about 0.20% magnesium wouldtherefore have to be introduced into the molten bath. The amountactually added to the bath would be even greater because in practicallyall cases, except when the more preferred magnesium addition agentsdescribed hereinafter such as the nickel-magnesium alloys containing 90%or more nickel and the nickelmagnesium-carbon alloys containing overnickel are employed, it is possible to obtain an introduction of only asmall amount of the magnesium added to the bath. This is apparently duemainly to its high volatility at the temperatures involved and also dueto its low solubility in iron.

Control of graphitizing factors An important consideration in carryingout the invention is the graphitizing power of the molten ferrous bathto be treated. Satisfactory baths or melts which may be treatedv inaccordance with the invention to produce a product having highproperties and the spheroidal form of gray-colored carbon in the as-castcondition are those which, before the introduction of magnesium, havesufficient graphitizing power to be clearly classified by those skilledin the art as gray cast irons if cast in sand molds or in the particularkind of mold to be employed if it is a different mold, at least afterinoculation such as is conventionally employed in producing bettergrades of gray cast iron. The aforementioned satisfactory baths includethose molten baths having such high graphitizing power that they wouldbe gray cast ironswhen solidified regardless of whether or not they wereinoculated. The bath should have such graphitizing power that, when castas indicated hereinbefore after inoculation, it would be substantiallyentirely devoid of massive carbides such as occur in white cast irons.The graphitizing power of the bath is the summation of a number ofpossible variable factors. The carbon content is one factor, i. e., fora given set of conditions graphitizing power increases rapidly as thecarbon content increases. The bath generally will contain over 1.7%carbon and may contain as much as 4.5% or even 5% of carbon. Preferably,the bath to be treated contains about 2% to 4.5% carbon. Baths and finalcompositions containing 2.5% to 4% carbon have given very satisfactoryresults. Silicon present in the initial melted charge and/or added priorto the magnesium introduction also imparts graphitizing power but not tothe same extent as carbon or as a late inoculating addition after themagnesium introduction and just prior to casting. As a very rough rulefor predicting the effect of carbon and silicon on graphitizing power,it can be said that silicon is about three-tenths or one-third aseffective in increasing the graphitizing power as carbon, i. e., that anincrease of 3% of silicon is equal to an increase of 1% of carbon. Itmust be understood that this is only an empirical approximation and isaffected by a number of other factors including the entire compositionof the bath, the type of charge employed and numerous other conditionswell known by those skilled in the art to iniiuence graphitizationduring the cooling from casting temperatures. The aforementioned moltenbath, before treatment in accordance with the invention to produce animproved as-cast product, will generally contain at least about 0.5%silicon, preferably at least about 0.8% silicon, and may contain as muchas 5% or even 5.5% or 6% of silicon, although the occasions when suchlarge amounts of silicon would be employed are rare in view of the factthat carbon is more eective in imparting graphitizing power and thatsilicon in large amounts at a given carbon level has a tendency toreduce the properties, especially the toughness, ductility and/ortensile strength. Silicon is a strong ferrite former, and for thisreason, it might be desirable to employ large silicon contents where amatrix containing a large proportion of ferrite is desired in theas-cast condition. After the magnesium treatment and any requiredinoculation, the bath will generally contain at least about 1% silicon,preferably at least 1.3% silicon, and may contain as much as 5% or 5.5%or even 6% silicon. Satisfactory results have been obtained in as-castproducts made from preferred baths which contained about 0.5% or 0.8% to3% or 3.5% silicon before magnesium treatment and inoculation, andparticularly with baths containing up to 2.25% silicon before treatmentand inoculation, e. g., baths containing 1%, 1.25%,1.5%, 1.75%, 2%, and2.25% silicon. After magnesium treatment and inoculation, whichintroduced additional silicon, these baths had final silicon contentswhen cast between about 1.0% and 4.5%, preferably at least 1.5% silicon.More preferably, the bath should have such a silicon content that, afterany additional silicon incorporated during the treatment with magnesiumor the inoculation, it will contain between about 1.5% and 2.5% or 3%silicon. Other elements which impart graphitizing power to the bath arewell known to those skilled in the art and include such elements asnickel, aluminum, etc.

In addition to the composition, many other factors also affect thegraphitizing behavior of the bath as is well known to those skilled inthe art of cast iron. Thus, the

nature of the mold in which the iron is to be cast is a factor, as therate at which it is able to extract heat affects the cooling rate whichin turn influences the graphitization. Likewise, the graphitizing poweror potential of a particular bath will operate less effectively whencast in small section sizes, e. g., one-half inch, than when cast inlarge section sizes, e. g., four inches or eight inches, even though thesame kind of mold is employed. The temperature of the mold in which thebath is cast, the degree of superheat of the molten bath, the pouringtemperature, the nature of the metallic raw materials employed in thecharge used to produce the bath and numerous other factors willinfluence graphitization. The composition of the bath to be treated inaccordance with the invention should be controlled in the light of thevarious factors well known by those skilled in the art to influence theamount of graphitization. A particularly responsive range of final bathcompositions having sufficient graphitizing power to ave-id, under mostpractical foundry conditions, the occurrence of massive carbides orincidental chills in sections of a/s in thickness or greater, is definedby the carbon limits 2.5% to 4.5%, the silicon limits 1.0% to 4.0%, andthe silicon content being so related to the carbon content that the sumof Si C' 3.1 4.5

is greater than 1.00. lt is desirable that within this range andespecially toward the lower limits of carbon and silicon, the alloyproduct be substantially free from tellurium and bismuth in order toavoid vagaries in graphitizing power and irregular tendencies towardchilling.

Iizocnlation The inoculation which accompanies or follows theintroduction of magnesium into the bath is another important aspect ofthe invention, except in certain rare cases when the bath has a Veryhigh graphitizing power, for example, such an excessive amount ofgraphitizing power that after the magnesium treatment it will producethe gray-colored, spheroidal form of carbon in the casting regardless ofwhether or not inoculation is used along with or after the magnesiumintroduction. If the inoculation precedes the introduction of themagnesium, it may not produce the desired results in the as-castproduct. This can be remedied by another inoculation along with butpreferably after the magnesium introduction. Inoculation may beaccomplished by a late addition of an inoculant such as silicon. 1t ispreferred to employ silicon in amounts between about 0.3% and 2% or2.5%, more preferably between about 0.4% and 1.2%, as the late additionto effect inoculation. lt has been found that if the treated bath isheld too long after inoculation, the inoculating effect wears off and islost. This can be compensated for by another inoculating addition whichmay incorporate a smaller amount of the inoculant, c. g., silicon. Aslittle as about 0.1% or 0.15% of silicon can be introduced tore-inoculate the bath, although, of course, larger amounts may beemployed. By periodically reinoculating the bath while maintaining therequired retained magnesium content, it is possible to cast a largetreated bath over a considerable period of time.

lt is preferred, in carrying out the present invention to produce aproduct having the higher order of properties and the spheroidal form ofcarbon in the as-cast condition, to introduce the magnesium into thebath and thereafter separately introduce the graphitizing inoculantwhich is preferably a silicon-containing inoculant, such asferrosilicon. While ferro-silicon, e. g., an iron alloy containing amajor proportion up to about or 95% silicon, gives satisfactory resultsas an inoculant, other metallic silicon-containing agents or alloys suchas nickel-silicon alloys or nickel silicide, calcium-silicon alloys orcalcium silicide, silicon metal, and various proprietary inoculatingalloys commonly used for reducing dendriticism and reducing chill infoundry gray cast irons may be employed. .es those skilled in the artknow, commercially available ferro-silicon and Various proprietaryinoculants usually contain calcium, e. g., up to about 1% calcium. It isalso known that ferro-silicon and various proprietary inoculants containaluminum. In by far the greater number of cases, it is essential thatinoculation be employed to produce the aforementioned product having thehigher order of properties in the as-cast condition. As magnesium hasbeen found to have by itself a very strong whitening effect, very fewmolten baths employed in actual practice can ce treated with magnesiumin accordance with the invention and cast without inoculation to producethe novel product of the invention or to obtain the novel combination ofproperties provided by the invention. As an empirical approximation,which may be employed to estimate whether or not a particular bath hassuch high graphitizing power that inoculation will not be required, itcan be said that when the carbon content of the bath plus one-third thesilicon content of the bath at the time of the magnesium introduction isapproximately 5% or more, then inoculation probably is not required butwould still be advantageous. Although, as stated hereinbefore, it ispreferred to inoculate the molten bath after the magnesium introduction,it has been found that certain baths having not quite as highgraphitizing power apparently can be inoculated prior to the magnesiumintroduction. For example, a molten inoculated bath containing 4% carbonand 2% silicon (including 0.75% silicon introduced for inoculation) justprior to the magnesium introduction did not require another andsubsequent inoculation although such an inoculation of part of the bathwas benecial and raised the transverse properties of the product.However, a similar inoculated bath containing about 3% carbon and 2.3%silicon (including 0.75% silicon introduced for inoculation) just priorto the magnesium introduction solidified as a white cast iron when castafter the magnesium introduction without additional accompanying orsubsequent inoculation. When a portion of this bath was inoculated afterthe magnesium introduction with 0.2% silicon and east shortlythereafter, the product of the present invention was obtained. As inpredicting the initial graphitizing power of the molten bath to betreated, it must be borne in mind that other factors, well known bythose skilled in the art to influence the graphitization of the bathwhen it is cast, should also be taken into consideration, e. g., thesection size of the casting to be produced, the kind of mold to beemployed, etc. As an illustrative eramole, a magnesium-treated moltenbath containing about 3.5% carbon and about 5 o silicon will notordinarily require inoculation although such treatment would bepreferred. Those magnesium- 'amazes treated baths not requiringinoculation will, in general, contain over 3% carbon. The presence ofhard, chilled corners or edges in a casting made from themagnesiumcontaining molten metal is an indication that the graphitizingpower is low but near the borderline. This low graphitizing powerordinarily should be compensated for by employing inoculation if it hadnot been employed or by using more effective inoculation or by otherwiseincreasing the graphitizing power or graphitization. For someapplications, it may be desirable to produce a product having a hardchilled surface portion or outer layer in which the carbon is in thecombined form to provide Wear resistance or the like while alsoobtaining in the product a core or body portion having substantialamounts of uncombined carbon in the spheroidal form and having theimproved properties provided by the invention. Such products may be madeby controlling the known factors which affect the amount ofgraphitizaton that will take place in the various portions of theproduct. It has been found that the magnesium-containing moltencomposition has a somewhat greater chilling propensity than has avsimilar magnesium-free gray cast iron composition but the chillingpropensity is affected to a lesser extent by lchanges in the carboncontent than is that of conventional gray cast iron. The treatedinoculated metal can be cast in accordance with accepted foundrytechnique, bearing in mind that the shrinkage characteristics of themolten alloy are such that castings made from the alloy should be gatedand risered more in conformity with the practice employed for steel thanthat employed for unalloyed or low-alloyed gray cast iron.

The molten composition employed in the present process may be free fromalloying elements or may contain substantial amounts of alloyingelements, e. g., nickel, molybdenum, chromium, manganese, etc. No commonalloying elements in the usual amounts employed heretofore in gray castiron, with the possible exception of large amounts of copper, have beenfound to prevent the results -of the invention from being obtained inthe as-cast condition. As will be apparent to those skilled in the art,the 'whitening or carbide-stabilizing properties of some alloy- .ingelements must be borne in mind in view of the re- Iquirement that thefinal bath treated in accordance with .the invention must possesssuicient graphitizing power when cast to produce a substantial amount ofuncombined carbon in cooling from pouring temperatures. For this reason,it is preferred that the chromium content normally not exceed about 1%,more preferably not over about 0.5% or 0.6%. However, the amount ofchromium that can be tolerated depends upon the composition of the finaltreated bath as a whole, and the maximum amount of chromium is thatwhich will provide a treated bath having the required graphitizingpower. Thus, satisfactory results were obtained in an as-cast austeniticferrous product produced in accordance with the invention whichcontained about 2% chromium in addition to about 20% nickel, 1.2%manganese, 2.2% silicon, 2.6% `carbon and 0.075% magnesium. Manganese, amilder whitener or carbide-stabilizer can be tolerated in largeramounts, and the results of the invention have been obtained withas-cast compositions containing up to about 2.5% manganese. Largeramounts of manganese can be present when the iinal cast alloy has anaustenitic composition or matrix. In general, manganese tends to lowercertain mechanical properties, especially in those as-cast :alloys inwhich the iron is in the alpha form, and it is :preferred that themanganese content not exceed 0.8% tor 1%. Higher ductility and toughnessare particularly :notable in such alloys when the manganese content does:not exceed about 0.3%. Aluminum decreases carbide stability and acts asa graphitizer. The term alloying eelements includes residual amounts ofthose elements :added as treating agents, degasiiiers, etc., and thoseele- :ments introduced along with the magnesium as carrier i'elementsfor magnesium or introduced by master alloys 10 containing magnesium.Copper should not be employed in large amounts as it has been found thatthis element when present in large amounts interferes with theformation, in the as-cast condition, of the spheroidal or spherical formof carbon required by the present invention. For this reason, it ispreferred that copper not be employed in amounts exceeding 3%, and morepreferably not exceeding 2%, without first determining the effect ofcopper upon the carbon formation in the particular composition. Certainalloying elements such as nickel may in conjunction with copper increasethe tolerance for the copper. It has been found that certain otherelements not usually found in cast iron should be avoided or should bepresent only in traces or very small amounts because they interfere withthe formation of the spheroidal form of carbon and/or the attainment ofthe high properties provided by the invention. These subversive elementsinclude tin, lead, antimony, bismuth, arsenic, selenium, tellurium, etc.It may be possible to compensate for the presence of a small amount ofthese subversive elements, preferably less than about 0.1%, byincreasing the amount of magnesium introduced into the bath and/or bythe introduction of specific elements to form compounds of highstability with the subversive element. The presence or addition of tinhas been found to be particularly detrimental, and the tin contentshould be kept below 0.1%, preferably below 0.05%. It is more preferredthat the bath and final alloy be devoid of tin. Phosphorus (which doesnot interfere with the formation of spheroidal carbon) is usuallyconsidered an impurity but may be added sometimes to obtain specificeffects. The phosphorus content may be as high as 0.5 or more, butpreferably should not exceed approximately 0.25% and more preferablyshould not be more than about 0.15%. Where high properties, especiallyimpact properties and/or ductility, are desired in the as-cast ferrousalloy, it is recommended that the phosphorus content not exceed 0.06%,for example, 0.02% to 0.06%. In the product produced by the processcontemplated by the present invention, the sulfur content is low,usually not exceeding about 0.02%, and is commonly between about 0.007%or 0.010% and 0.015% unless the raw materials and/or the processemployed in producing the product introduce less sulfur. Obviously, thelower the amount of subversive, detrimental or interfering elements, thelower the amount of magnesium that need be introduced and retained. Thebalance of the composition of the bath and of the magnesium-containingproduct is iron (including small amounts of impurities, preferably lessthan a total of about 0.5 In most eases, the magnesium-containingproduct will be unalloyed or lowalloyed and the iron content will be atleast about or 87% by weight of the total composition. In the case ofthe more highly alloyed compositions, usually having an austeniticmatrix, the iron content may be considerably lower than 87% but will beat least 50% or 55%. The process embodying the present inventioncontemplates the production of as-cast cast iron compositions havingferritic matrices, martensitic matrices (such as described in U. S.Patent No. 2,324,322), austenitic matrices (such as those containing 21%or 29% or 36% nickel, etc.), etc.

Introduction of magnesium The introduction of the essential amounts ofmagnesium required by the present invention can be accomplished in anumber of Ways. However, the amount of magnesium to be added to the bathwill depend upon the retained magnesium desired, the additional amountof magnesium required to overcome the presence of interfering elementssuch as sulfur, etc., the amount of magnesium lost by delaying thecasting of the bath after the introduction of the magnesium and theproportion of magnesium recovered in the hath from the magnesiumaddition agent. The last factor involves the losses of magnesiumincurred in attempting to introduce the magnesium into the molten bath.This last factor presents considerable ditiiculties, as it has beenfound that in many cases no magnesium can be recovered from the additionagent employed or only a small amount recovered, e. g. 3% of the amountadded. The art has taught that magnesium docs not alloy with iron, andas a matter of fact, when it has been attempted to introduce metallicmagnesium in elemental form into a molten bath of iron when the latterwas at the ordinary elevated temperature required for satisfactorycasting, a reaction of l such explosive violence took place that themolten iron was blown from the receptacle in which it was held. Inaddition, it is known that the temperatures of molten iron baths usuallyexceed the boiling temperature of magnesium. The fact that theintroduction of elemental magnesium into molten iron baths produces areaction of explosive violence has been well recognized in the artheretofore, and the introduction of magnesium into molten iron has beengenerally regarded as being irnpossible on a practical scale. Proposalshave been made by the prior art to solve an analogous problemencountered in the introduction of various highly volatilizable elementsinto molten baths, for example, U. S. Patent No. 1,931,144 relating tothe introduction of sodium as sodium vapors into a molten bath to purifythe bath. lt has been found that magnesium in the form of a solidmagnesiu11i-containing agent can be added in a number of ways tointroduce into the molten bath magnesium in a form capable of acting asif it were introduced in elemental form, for example, in a formavailable to react with sulfur, such as the sulfur which is usuallypresent in the molten carbon-containing ferrous bath being treated inaccordance with the process of the invention. Metallic magnesium can beadded with due caution in solid elemental form directly to the moltenferrous bath when the bath is cold, i. e., at a temperature not farabove the liquidus temperature of the molten composition, e. g., about2250 to 2400 F. The temperature should be only sufficiently high for themolten bath to be completely molten but viscous. Such an addition ofelemental magnesium is accompanied by the burning of the magnesium onthe surface of the molten bath with consequent brilliant flashing,evolution of large quantities of magnesium oxide smoke and the loss ofby far the greater portion of the magnesium added. However, recovery ofsutlcient retained magnesium to obtain the effect on carbon occurrencein the alloy contemplated by the invention can be accomplished by thismethod if a sufiiciently large amount of magnesium is added. It isimportant in using this method, however, that the temperature not be fitoo high and/or that it not be endeavored to submerge completely andhold the magnesium below the surface of the melt, in order that theattendant reactions not be excessively violent. When this method isused, the

temperature of the melt after the magnesium introduction is thenpreferably quickly elevated to about 2500 F. or higher to increase theuidity of the bath, to enable it to reject non-metallics and to insure asound casting when the bath is cast. After elevating the temperature ofthe bath, it is inoculated, e. g., with about 0.3% or more of silicon7and then cast in an inoculated condition. Magesium may also be added inthe form of briquettes with binders and the like to decrease the burningof the magnesium and to allow the magnesium to become incorporated morequietly and with greater recovery of the magnesium in the bath. Ofcourse, briquettes may also be employed to introduce the magnesium inthe other forms described herein, e. g., as magnesium-containing alloys.

It is preferred to add the magnesium as a metallic agent, such as analloy, containing about 2% to about 4050 magnesium. Suitable alloysinclude those alloys which are sometimes referred to as intermetalliccompounds, e. g., MgNiz, or mixtures of an intermetallic compound with ametal or with another intermetallic compound, e. g., MgNiz-l-Ni orMgNiz-l-MgzNi. It has been found desirable to introduce the magnesium asan alloy with one or more metals in which the magnesium is soluble inthe molten condition, these metals in turn being soluble in iron in themolten condition. In carrying the invention into practice, nickel,copper and/or silicon are the preferred metals with which the magnesiumis alloyed to form the addition agent. The usefulness of copper issomewhat limited due to the desirability of maintaining the coppercontent of the nal product relatively low as indicated hereinbefore, e.g., below approximately 2%. The copper concentration of the additionalloy should be such that it will not introduce excessive copper.Likewise, high silicon contents in the final product, e. g., 5% or 6%,or usually undesirable because of their adverse effect on the mechanicalpropcrties of the final product, and this restricts the usefulness ofthe high-silicon addition alloys although the final product will containthe required spheroidal form 0f carbon. In practice, very satisfactoryresults have been obtained with binary and more complex alloys of nickeland magnesium. Preferably, the magnesium should be introduced as analloy which has a density approaching that of the molten bath orexceeding it, as it has been found that the greater the density thegreater the proportion of the magnesium recovered in the molten bathunder a given set of conditions. A series of alloys which have givensatisfactory results are the nickel-magnesium alloys containing fromabout 4% to about 20% magnesium. It has been found that when thenickel-magnesium alloys also contain carbon, for example, up to themaximum amount that the alloys will take up, the additioncharacteristics of the alloys, especially those containing about 10% to15% magnesium, are improved. Furthermore, by iirst producing a moltennickel-carbon alloy and then introducing magnesium therein, themanufacture of a nickel-magnesium addition alloy is facilitated.Nickel-magnesium-carbon alloys containing 10% to 15% magnesium andcontaining carbon within the range of about 1% to 4%, preferably about2% to 4%, have given good results when used as addition agents.

In general, the higher the concentration of magnesium in the additionagent the lower the proportion of magnesium introduced into the moltenbath. Various means may be employed to increase the proportion ofmagnesium introduced into the bath for any given composition, but thehigh reactivity of magnesium should always be borne in mind. The lowerthe temperature of the moldten bath at the time of the magnesiumintroduction, whether as an alloy or in another form, the higher will bethe proportion of magnesium introduced from a given agent. Likewise, theproportion of magnesium introduced can be increased by blowing apulverulent or powdered magnesium-containing alloy through a tube or thelike into the molten bath below the surface thereof by means of a gaswhich is inert or non-oxidizing with respect to magnesium. Theproportion of magnesium introduced into the molten bath from a givenmagnesium-containing alloy of lower density than the molten bath beingtreated can be increased by submerging the addition alloy below thesurface of the bath, e. g., by adding crushed addition alloy to a moltenstream of the metal bath being poured into a ladle. From the standpointof ease of introduction of magnesium, the 96% nickel4% magnesium alloyis very satisfactory because this alloy has about the same density asthe molten bath and tends to sink therein so that substantially noburning of magnesium occurs. Because of the high nickel concentration ofthis addition alloy, substantial amounts of nickel are also introducedin the molten bath and carried over into the nal product. As themagnesium concentration in the nickel-magnesium alloys is increased, theburning and loss of the magnesium is increased since the alloys becomeprogressively less dense and are less immersed in the molten bath. Good,reasonably economic alloys suitable for introducing magnesium into themolten bath are (l) an alloy containing 13 Y t approximately magnesiumand approximately 90% nickel and (2) an alloy containing about 12% to15% magnesium, about 2% to 4% carbon and the balance essentially nickel.Of course, other magnesium-containing alloys can be employed. Thus, thenickel-magnesium alloys may also contain other elements such as silicon,manganese, copper, iron, etc., but it has been found that, in general,the proportion of magnesium introduced into the molten bath from theaddition alloy increases as the nickel content of the addition alloyincreases. For example, replacing part of the nickel by iron usuallydecreases the proportion of magnesium introduced from the additionalloy. The following Table I sets forth the approximate composition ofsome magnesium-containing alloys which can be employed as additionagents for the purpose of introducing magnesium into the molten bathinthe amounts required by the invention.

TABLE I Percent S1 Gu Per- Percent Percent Percent Percent C Mn FeOthers An unusual feature of the invention is that the magnesiumtreatment very effectively removes sulfur from the molten ferrous batheven when it is under the inuence of acidic conditions such as createdby furnace 1inings, ladle linings, slags, etc., of a siliceous nature orother acidic nature as well as under neutral o1' basic conditionscreated by the furnace lining, the ladle lining, the slag, etc. Anotherunusual feature of the invention is that the removal of sulfur by themagnesium treatment does not require the presence of any slag and takesplace regardless of Whether a slag is or is not present. For example,sulfur can be removed by the magnesium treatment from a molten ferrousbath while it is not covered by a slag and while it is being held in anacid-lined ladle or other acid-lined contained.

The essential features of the novel product produced by the inventionare the presence of carbon, and usually silicon, in amounts within thecast iron range, the presence of a substantial amount of the carbon inthe uncombined form, and the presence of a small but eifective amount ofretained magnesium with the remainder essentially iron to provide anas-cast ferrous matrix in which the soft, gray-colored spheroids ofuncombined carbon are dispersed. In other words, the novel productprovided by the process embodying the present invention contains a smallbut effective amount of magnesium, for example, about 0.04% or moremagnesium, with the balance of the alloy being a gray cast ironcomposition. All the carbon present in the product provided by theinvention need not be uncombined carbon present in a spheroidal form.Thus, micro-constituents of the ferrous matrix (which may be pearlite,martensite, austenite, bainite, etc.) usually contain combined carbon.In general, less than half of the carbon present in excess of thatrequired to produce the matrix structure will be combined carbon in theproduct produced by the invention. The uncombined carbon will be presentas compacted particles, at least some of these particles and morepreferably most or even all of the particles occurring in asubstantially spheroidal or spherical, soft, gray-colored form. Theoccurrence of some of the carbon in the very compact substantiallyspheroidal or spherical form in the as-cast condition is accompanied bya compacting of the remaining uncombined carbon, but this compacting maybe to a lesser extent. This compacting, including the presence of about25% or more of the uncombined carbon as spheroids or spheres, indicatesthat a notably improved combination of properties will be obtained.

The product produced by the process embodying the present inventioncontaining the spheroidal form of carbon in the as-cast condition hassuch a remarkable combination of properties, as compared to those ofcast iron, cast steel and pearlitic malleable iron, that it can beclassified as a completely new ascast ferrous alloy and provides the artwith a new metallic engineering materi-al. The as-cast alloy hasexcellent founding properties, e. g., it can be readily cast into moldsof intricate design, the molds being made of the usual materialsemployed in molds for casting cast iron. The molten alloy has bettercastability than steel and has a castability comparable to, or evenbetter than, many grades of cast iron, especially the higher qualitygray cast irons which, in order to develop high mechanical proper-ties,are limited to the lower carbon and silicon contents of the cast ironrange. The as-cast alloy produced by the process embodying the inventionhas the desirable property of being strongly self-feeding in the mold,thus providing an automatic check on the quality of the castings made ofthe new alloy because improperly fed castings often will be misshapenand will exhibit depressed or shrunken regions on the surface. Theproduct produced by the invention has an exceptionally high combinationof strength and ductility in the as-cast condition and in this respectis far superior to any cast iron of comparable composition availableheretofore. The new product possesses unique elastic properties notpossessed by gray cast iron (for example, a straight-lineproportionality of stress to strain over a wide range of stresses, ahigh proportional limit and a consistently high tensile modulus ofelasticity of about 25,000,000 pounds per square inch or greater),resistance to the combined effects of oxidation and heat (e. g., growthresistance) superior to that of gray cast iron, and other improved orhigh properties. In general, the tensile strength of the as-cast productwill be more than about 50% greater than would be obtained in the samecomposition not containing magnesium, and usually the improvement intensile strength will be or much more, e. g., the tensile strength willbe increased over that of the base composition by at least about 40,000pounds per square inch or much more. In the pearlitic compositions, hightensile strengths on the order of 85,000 pounds to 120,000 pounds persquare inch, or even more, are produced in combination with elongationsas high as 5% or even more. The properties possessed by the productprovided according to the invention are dis closed in detail in ouraforesaid Patent No. 2,485,760.

The product provided by the method embodying the present invention maybe produced from the usual ferrous raw materials employed in theproduction of gray cast iron. For example, the novel product can be madefrom a charge comprised of pig iron as the ferrous raw material. Theusual furnaces employed in the production of gray cast iron or malleableiron can be employed in carrying out the process embodying the presentinvention. Thus, the cupola furnace commonly used in an ordinary foundrycan be employed very advantageously in carrying out the inventionalthough other furnaces, e. g., the -arc or induction electric furnace,ythe air furnace, etc.,

may be employed. Duplex melting operations may also be employed. Aspointed out hereinbefore, the operations can be carried out underacidic, neutral or basic conditions created by furnace linings, ladlelinings, the slags, etc.

Herzt treatment When it is desired to enhance certain particularproperties or to modify the combination of properties possessed by thealloy provided according to the present invention, it may be subjectedto known heat treatments, including induction hardening, flame hardeningand similar surface treatments, to atect particular properties orcombinations of properties of ferrous alloys. Thus, the alloy producedby the process embodying the invention can be subjected to heattreatments for stress relief, strengthening, hardening, toughening, etc.These heat treatments include so-called iso-thermal treatments oraustempering treatments of ferrous alloys to transform austenite,including any retained austenite, to an acicular constituent at or nearthe temperatures corresponding to the nose of the S-curve or below saidnose but above the martensite transformation temperature. Otherillustrative heat treatments which may be employed to modify somewhatthe properties of the as-cast alloy of the invention include quenchingand drawing, normalizing and drawing, etc. For example, the product canbe reheated above the critical transformation temperature, then cooledin air or quenched in oil or water, and then drawn at about 400 F. toabout 1250 F. illustrative examples of various heat treating proceduresand the properties resulting therefrom are set forth in our aforesaidPatent No. 2,435,760.

A special heat treatment has been found which produces markedly improvedductility in combination with high tensile strength in as-cast alloyshaving a pearlitic matrix. This heat treatment involves treating apearl'itic cast alloy within a range of temperatures slightly below thelower critical temperature, generally for at least about one hour. Inpractice, it is preferred to employ temperaturcs not more than 75 F.below the critical transformation temperature of the composition beingtreated and more preferably not more than 50 F. below said criticaltemperature (often also referred to as the critical point or the A1point, i. e., the lowest temperature where the alpha-gammatransformation takes place in the particular composition involved). Itis also preferred that the heat treatment at an elevated temperatureslightly below the critical temperature be conducted for at least abouttwo hours. An advantage of this treatment at relatively low temperaturesis that it can be carried out in comparatively short periods of time butthere are no particular limitations on t'ne maximum time of treatment.Treating times up to fifteen or twenty hours have given satisfactoryresults, e. g., tive hours or ten hours.

It has been found that the aforementioned special l heat treatment ofthe magnesium-containing, as-cast ferrous alloy having a pearlitiematrix at atmospheric temperatures and containing the spheroidal form ofcarbon produces an improved combination of properties, especially animproved combination of ductility and tensile properties, as compared tothe properties of malleable iron, e. g., standard or ferritic malleableiron. Because the aforementioned special heat treatment has aferritizing ciiect on the matrix, this heat treatment has been referredto as a ferritizing treatment and the product as a ferritized product.After the ferritizing heat treatment of the present invention, themagnesium-containing product has a microstructure comprisedpredominantly or even substantially entirely of a ferrite matrixcontaining compacted and dense, randomly dispersed, substantiallyequiaxed particles of uncombined carbon, preferably spherulitoid,spheroidal or spherical in shape. The structure of the heat treated orferritized product of the invention is preferably substantially freefrom flake graphite. Generally, no sulfide particles appear in thematrix, whereas ordinary gray cast irons, white cast irons, andmalleable irons contain many easily recognized sulfide inclusionsembedded in the matrix. The spherulitoid or spheroidal particles in theferritized product of the invention are soft and gray-colored and arecomprised of a large spheroidal or spherical body with a very thinirregular fringe, shell, edging or rim as shown in Fig. 6. Under highmagnification, e. g., a magnificaof 1000 diameters at which theparticles are usually about 1 to 21/2 inches in average diameter, thespherulitoid or spheroidal particles are generally characterized by aradiating or radial type of structure in the body portion, which isapparently composed of a plurality of crystals radiating from one ormore points near the center of the particle. The fringe or edging, whichis very thin, has a rougher and pebbly appearance. This edging or fringedoes not necessarily appear around the entire circumference of the bodyportion of the carbon particle.

The ferritized alloy provided by the present invention usually containsover about 1.7% but less than 5% carbon, over 1% but less than 4%silicon, and magnesium usually within the range of about 0.04% to 0.25%or 0.3%. A feature of the composition is that it can have a highgraphitizing power such as cannot be present in compositions employed toproduce malleable iron. Compositions having such high graphitizinz powerthat the carbon content plus one-third the silicon content is over 3.5%or 3.7% can be employed to produce the ferritized alloy of the presentinvention as well as compositions having lower graphitizing power. Manyas-cast compositions in which the carbon content plus one-third thesilicon content was 4.2% or more have been treated very satisfactorilyto produce the heat treated ferritized product of the present invention.in producing the ferritized alloy, it is preferred to maintain thecarbon content within the range of 2% to 4.5%, to maintain the siliconcontent within the range of 1.3% to 3.5%, more preferably within therange of 1.5 /b to 3%, and to maintain the magnesium content within therange of 0.05% to 0.2%, especially within the range of 0.06% to 0.15%.The fact that silicon contents above 1.5% and/or carbon contents above3% can be employed in part distinguishes the ferritized product of thepresent invention from high quality malleable iron which has beenrestricted to low silicon contents, usually not over 1.2% (e. g., 0.8%to 1.2%), and/or low carbon contents, usually not over 2.7% (e. g., 2.0%to 2.7%). Most of the carbon, and often essentially all the carbon, willbe uncombined and will be present in the spherulitoid or spheroidal formof uncombined carbon in the ferritized alloy of the present invention.In some instances, for example, when the heat treatment has not beenconducted for a sufliciently long time and/ or when the compositioncontains a substantial amount of carbide stabilizers such as chromium,manganese, etc., a minor proportion of combined carbon or carbides maybe present in the final ferritized product. Retained magnesium in theamounts contemplated by the invention has been found to have a verystrong whitening effect and to have a tendency to refine pearliteslightly. Although magnesium has a whitening effect, the ductilemagnesiumcontaining ferritized product of the present invention can beobtained from the as-cast product of the invention with a considerablyshorter heat treatment than is required to obtain ferritic malleableiron. The ferritized alloy may be free from alloying elements or maycontain small amounts of alloying elements, particularly nickel. Thus,the alloy to be ferritized may contain the small amounts of nickel,molybdenum, chromium, manganese, etc., that permit obtaining a pearliticmatrix in the as-cast product. The nickel content is preferably lessthan 4%, e. g., 0.5% to 2.5% or 3%. Molybdenum stabilizes austenite and,in addition, tends to increase the heat treating time required. It ispreferred that chromium be absent, although amounts of chromium notexceeding about 0.5% or 0.8% may be present. Manganese preferably doesnot exceed 0.8% or 1%. Manganese is an austenite stabilizer and, likechromium, interferes to some extent with the ferritizing heat treatment,usually by increasing the heat treating time required, and for thisreason is more preferably maintained below 0.4% or 0.3%. It is preferredthat copper not be present in large amounts, e. g., in amounts exceeding2%. While phosphorus may 'be as high as 0.4% or 0.5%, it preferablyshould not exceed 0.25% and more preferably not more than about 0.06%,as it has been found that phosphorus tends to lower the properties ofthe ferritized product, especially the ductility and the tensilestrength. Due to the presence of magnesium in the product, the sulfurcontent is low as pointed out hereinbefore. For the reasons set forthpreviously, the product should be substantially devoid of or shouldcontain only very small amounts of the subversive elements referred tohereinbefore. The balance of the composition is iron except for smallamounts of impurities. The iron content, in general, willbe at leastabout 87% and will usually be at least 90% of the total composition. Thefinal heat treated ferritic product made in accordance with theinvention and having the foregoing compositions will have the structuredescribed hereinbefore. v Y

The ferritic product produced by the special heat treatment and havingthe aforementioned composition and microstructure is distinguished fromferritic malleable iron by an improved combination of foundingproperties, strength and ductility. Usually, the ferritized castings ofthe invention possess high ductility which is evidenced by `anelongation in tension of over 5% and as high as 20% or more. The highductility is obtained in conjunction with higher strength than has beenobtained in malleable iron and similar alloys. The high ductilitycombined with high strength can be obtained in compositions containingmore carbon and/or silicon than has been employed in malleable iron.Another feature of the ferritized alloy is that it can be produced inlarge section sizes, e. g., up to 4 or 5 inches or even more, withoutunduly sacrificing properties or appreciably increasing the heattreating time required and is not limited to the small section sizes, e.g., up to 1 inch and on occasion up to about 2 inches, which restrictthe pro duction of malleable iron products. For example, it has beenrecognized that increasing the section size up to about 2 inchesconsiderably lowers the properties of malleable iron or increases theheat treating ltime required to produce the same. In addition,a'requirement of malleable iron is that it be made from a cast ironsubstantially devoid of uncombined carbon in the as-cast condition, i.e., a white cast iron free from lprimary graphite, whereas theferritized product of the present invention is made from amagnesium-containing ferrous alloy having a substantial amount ofthetotal carbon content present in the uncombined form in thev as-castcondition. In actual practice, particularly satisfactory results havebeen obtained in ferritized products containing about 2.8% to about 3.8%carbon, about 1.5% to about 2.7% silicon, about 0.06% to about 0.15%magnesium, about 0.5% to about 3% nickel, about 0.1% to about 1%manganese, and the balance essentially iron, particularly when themanganese content does not exceed about 0.3% and the phosphorus contentdoes not exceed about 0.05%. Ferritized products having compositionswithin the aforesaid range, i. e., the most preferred range ofcompositions, will generally have the following average properties:

Yield strength 45,000-55,000 p. s. i. (0.2% offset) Tensile strength63,00075,000 p. s. i.

Elongation.. 12 to 18% Hardness 150 to 190 Vickers number j Table'IIsets forth data showing the new combination of properties that wereobtained in alloy 29 (see Table III) after a ferritizing treatment (No.4) for ve hours at l300 F. as compared to the properties possessed bythe pearlitic product in the as-cast condition.

TABLE II Property As-cast Ferritized Percent Elongation (2 in.) 20. 5Percent Reduction of area 6. 4 17. 6 Yield strength (0.2%), p. s. i. 60,100 48, 500 Tensile strength, p. s. i.. 96, 300 66, 100 Vickers hardness23 181 final heat treated product and compensates for possible variablesof production in the initial casting. The higher temperature treatmentis satisfactorily accomplished Vby subjecting the castings to one ormore temperatures between about 1800 F. and the critical temperature,preferably for at least about one hour and more preferably for at leasttwo hours. There is no particular'limitation upon the maximum time attemperature in this treatment, but generally satisfactory results areobtained in less than about 15 hours, e. g., in about 3 to 5 hours. Asuitable treatment comprises subjecting the casting to temperaturesbetween about 1750 F. and 1500o F. This higher temperature treatmentwhich precedes the lower temperature treatment can be effected byholding the casting at one or more temperatures and then cooling at anyconvenient rate, or by gradually cooling the cast-` ing through therange of temperatures. Such a gradual cooling treatment is obtained byfurnace cooling, pit cooling, or even cooling in the mold when the massis sufficiently large to maintain a slow cooling rate. Average coolingrates of about to 200 F. per hour, e. g., about F. per hour, through therange of temperatures down to the critical temperature can be utilizedas the vhigher temperature treatment to produce satisfactory results.The foregoing treatment can be accomplished in a number of ways. Forexample, in one method which utilizes the heat contained within the hotcasting, these hot castings are stripped from their molds at red orblack heats, transferred to a preheated pit at 1400 F. to 1800 F., e.g., 1500 F. to 1750 F., and allowedto cool slowly in the pit until thetemperature is slightly below the critical temperature, at which pointthe cooling -is interrupted and the castings held at thatl temperaurefor the required time. Alternatively, cold pearlitic castings can beplaced in the preheated pit and held for the required time to raise thetemperature to within the range of 1400 F. to 1800 F. and then treatedin the same manner. Cold castings can also be transferred to a furnaceor pit and held at a temperature between 1400 F. and 1800 F., e. g.,1550 F. or 1600 F. or 1700 F. or 1750 F., then air cooled or quenched,e. g., to room temperature or to just below the critical temperature,and then treated at a temperature or within the range of temperaturesjust below the critical temperature. In general, a temperature range(for treating just below the critical temperature) of about 1270 F. to1310 F. has given satisfactory results in treating most compositions inaccordance with the invention. Instead of holding the casting at onetemperature or a plurality of temperatures just below the criticaltemperature and/ or instead of interrupting the cooling from above thecritical temperature when a temperature just below the criticaltemperature is reached, satisfactory results can be obtained by slowlycooling the casting through the range of temperatures just below thecritical temperature, e. g., furnace cooling, pit cooling, or even bycooling extremely slowly in a mold. Slow cooling rates of 50 F. perhour, more preferably 25 F. or 30 F. per hour, or slower, can be used incooling through the range of temperatures slightly below the criticaltemperature without interrupting the cooling or Without holding thecasting at one or more xed temperatures. The critical temperature isiniiuenced by many factors, as is well known to those skilled in theart. For example, each composition has its own critical temperature. Thetemperature range set forth hereinbefore is generally suitable for mostcompositions but may have to be adjusted under particular conditions.Thus, silicon usually raises the critical temperature while nickellowers the critical temperature. Accordingly, if the nickel content ishigh, slightly lower temperatures should be employed, while if thesilicon content is high, slightly higher temperatures should beemployed. Nickel and/or silicon may occasionally be present in thecomposition in amounts which may require an adjustment in the treatingtemperature in order to maintain said treating temperature just belowthe critical temperature as described hereinbefore.

The inuence of the ferritizing treatment on the matrix of themagnesium-containing as-cast alloy produced by the process embodying thepresent invention is illustrated in Fig. 7. Fig. 7 shows the polishedand etched structure at a magnication of 250 diameters of acupolamelted, magnesium-treated, inoculated gray cast iron compositioncontaining about 3.6% carbon, 2.3% silicon, and the required amount ofretained magnesium to provide the spheroidal form of carbon in theas-cast condition after a ferritizing heat treatment comprising coolingslowly in a furnace from 1700 F. to 1280 F. and holding at 1280 F. forve hours. As illustrated by the etched structure in Fig. 7, the pearlitein the matrix has been converted by the heat treatment to ferrite.

In order that those skilled in the art may have a better understandingof some of the preferred embodiments of the ferritizing heat treatmentand of the properties that can be obtained in the ferritized productproduced according to the process embodying the present invention, datahave been set forth in Tables III, 1V, and V giving the composition (thebalance being iron except for small amounts of impurities), theferritizing heat treatment and the properties of ferritized productsmade in accordance with the invention from magnesiumcontaining ferrousalloy castings containing the spheroidal form of carbon in the as-castcondition.

TABLE IH Percent Percent Percent Percent Percent Percent Alloy No. Mg MnP Ni 2. 4 2. 1 0. 067 0.07 0.02 l. 3 3. 3 2. 7 0. 058 0.8 0.02 1. 62.1 1. 9 0. 078 0.8 0. 01 1.9 2. 4 1. 0 0. 000 0. 07 0.02 1. 9 2. 6 2. 30. 072 0.9 0. 0T 1. 9 3.1 2.1 0. 031 0.8 0. 06 1. 9 3. 4 2. 0 0. 058 0.80. 02 1. 9 3. 4 2. l 0.079 0.13 0. 02 l. 9 3.5 2. 3 0. 074 0. 1-0. 2x11. d. 2. 0 3. 5 2. 4 0. 066 0. 8 0.02 1. 9 3. (i 1.6 0. 001 0. 80.02 1. 9 3.6 2.1 0. 075 0. 09 0.02 1. 9 3. 7 1.1 O. 049 0. S 0.02 1. 93.8 1.4 0.050 0.8 0. 08 1.9 3.8 1.9 0.083 0.8 0.02 1.9 4.2 2. 3 0. 05%0.5 0.03 2.3 3. 4 2. 4 0. 019 0. 18 0. 04 2. B 4. 2 2. 3 0.002 0. 5 0.03 3.0 3. 4 2.1 0. 055 0. 8 0.02 3.1 3.6 2. 3 0.10 0.17 0. 04 3.6 3. 62. 3 0. 084 0. 73 0. 04 3. 6

1n. d.-Not determined, low.

TABLE IV No. Heat Treatment 5 0 .As cast (no heat treatment).

5 Cold castings heated t0 about l,750 F., held 5 hrs., furnace cooled toroom temperature, reheated to about 1,300" F., held 5 hrs.

6 Cold castings heated to about 1,700 F., held 15 ruin., fur

nace or pit cooled to about 1,280" F., held 5 hrs.

7 Red hot castings (stripped from mold) furnace or pit cooled from about1.700o F. to about 1,275 F., hc1d2 hrs.

8 Red hot castings (stripped from mold) furnace or pit cooled from about1,700 F. to about 1,275 F., held 5 hrs.

9 Cold castings normalized by holdingfor 1 br. at about 1,550: F. andair cooling to room temperature. reheatcd Lo about 1.300 F.. held for 5hrs.

.10 Cold castings heated to about 1,550 F. and held for 1 hr.,

quenched in oil, rehcated to about 1,300c F., held for 5 hrs.

TABLE V Treat- Alloy No ment No. El. R. A. VJIN Y. S. T. S

0 1. 5 336 33,500 96.500 5 14.0 14.0 190 52,500 a0, 200 6 12. 0 11. 4137 54,500 73,100 5 19. 0 19. 6 195 54. 400 73. 300 0 1. 0 1. 1 347 34,500 109, 500 5 16. 0 13.0 223 55,500 92, 000 0 0.5 321 70,000 94,500 5s. 0 9 3 218 57,000 93, 400 6 8.5 9 3 139 52,000 72, 400 0 0. s 296 7B,000 89, 200 5 s. 5 7. 1 201 47, 500 73, 100 6 8. 5 8. 2 210 57,00075,300 18 9 7. 5 6. 7 222 63, 000 80, 900 10 6. 5 6. 0 222 63, 500 83,200 0 1. a 2. 3 299 71,000 100. 300 6 7. 0 8. s 186 54,000 67. 300 9 13.0 10. 9 197 5s, 500 75, 000 0 5. 0 4. 9 23s 62, 500 100,000 5 15. 0 14.6137 4s, 000 70,000 6 13. 5 13. 0 192 40,000 72, 400 0 4.0 4.4 59,00093,000 5 17.0 19. 6 155 45, 000 03, 800 0 7. 0 6. 4 23s 60. 100 90, 3005 22. 5 21. 3 167 47, 400 04, 500 6 21. 5 21. 5 168 46. 300 64. 000 0 5.0 8. 9 258 67,000 100,000 5 17. 5 15. 6 179 52, 000 72,000 6 16. 0 17.1192 56,000 74,700 0 3. 0 2. 3 220 66, 000 110,000 5 13. 0 14. 5 175 43,500 71,000 0 5.0 4.4 234 60,000 98,000 6 18. 5 15. 6 150 46, 500 63, 9007 13. 0 9. 8 17s 49,500 6a, 500 0 1.0 1.1 303 64, 500 83,200 5 11. 010.2 180 41,000 72, 900 0 2. 5 2. 2 272 03, 500 95, 300 5 11.0 11.3 16143,000 64,800 0 2. 5 2. 7 238 7s, 000 108, 200 5 12. 5 13. 0 167 49, 50072, 300 5 10. 5 12. 5 51,000 67, 400 0 2.5 63,000 79,150 5 6.0 49,5000,000 5 6.0 59,200 72,000 0 5 6.1 203 52,000 71,600 0 3.3 30s 91,000121,500 5 10. 3 211 66, 500 S5. 500 6 14. 1 202 07,000 78,000 8 15. 6197 53, 500 76,400 0 1. 7 340 100,000 128.100 5 8. 7 244 76,500 94. 700

R. A.=Percent reduction of area. See footnotes of Table VI for key toterms, etc.

The improvement in ductility obtained by the ferritizing heat treatmentis illustrated in Fig. 8 which depicts photographs of originallystraight bend-test specimens,

about 6 inches long, after said specimens had been subjected to a bendtest to determine their ductility to the point of fracture. All threespecimens were made of alloy 29. The top specimen shows the highductility of the aS-cast alloy. The middle specimen shows the ductilityof the alloy after having been given heat treatment 6.

The marked improvement in ductility over the as-cast ductility is shownby the greater amount of bend withstood by the specimen before cracking.The bottom specimen shows the ductility of the alloy after having beensubjected to heat treatment 5.

By varying the ferritizing treatment, e. g., the temperatures, the timeof treatment, etc., it is possible to obtain various diierentcombinations of ductility and strength.

In general, as the ductility is increased, the strength propertiesv ofthe heat treated casting are decreased and v.vice versa. Thus, theductility Will usually be higher the longer the treating time just belowthe critical temperature lof the composition. This effect of varying thetreating time is illustrated in Table VI which shows the effect on theproperties of alloy 32 of a heat treatment comprising heating coldcastings made of said alloy to about l700 F., furnace cooling (e. g.,cooling at an average rate of about 80 F. to 100 F. per hour) to about1275 F., and holding at the latter temperature for the various periodsof time indicated in Table VAI.

E1.=Percent elongation iu 2 inches.

R. A.=Percent reduction of area.

VHN=Vickers Hardness Number.

Y. S.=Yield strength (0.2% offset) in pounds per square inch. T.S.=Tensile strength in pounds per square inch.

As indicated by the foregoing data in Table VI and by the data in TablesIV and V, a high combination of properties, particularly-high ductility,can be obtained by a ferritizing heat treatment in which the total timeof treatment required is short. The data presented herein illustrate thesatisfactory results that can be obtained by the ferritizing heattreatment of the present invention in a total time, including a hightemperature treatment, of about 5 to 16 hours. In many cases,particularly those in' which the more preferred maximum amounts ofmanganese, chromium and other stabilizing elements are not exceeded (andin which other carbide stabilizing factors are not dominant), asatisfactory combination of properties can be obtained by treating hotcastings for about two hours at 1275 F. to 1300 F. When a partiallypearlitic or spheroidized matrix structure is required, as, for example,where somewhat higher strength with a moderate increase in ductility isdesired, the total time of treatment can be shortened. For practicalpurposes, the pit cooling treatment referred to hereinbefore, e. g., inT able IV, is a particularly satisfactory treatment because it can becarried out in the simplest equipment.

- It has been indicated hereinbefore that the phosphorus content of theferritized casting is preferably maintained low, Increasing amounts ofphosphorus have been found to lower the properties of the ferritizedcasting, particularly Ithe tensile strength and the ductility (which isindicated by elongation and/ or reduction of area).

It is also preferred that the manganese content of the ferritizedproduct be low, e. g., not more than 0.3% or 0.4%. Manganese apparentlystabilizes carbon in the form of carbides, for examplein the pearlite ofthe matrix, because as the manganese content increases, longer treatingtimes below the critical temperature are required to obtain similarstructures. Likewise, it is preferred that the silicon content of theferritized product not be too high. It has been found that high siliconcontents detrimentally affect the properties, particularly theductility. Silicon in amounts from about 1% to about 3% does not appearto have any detrimental effect on the properties and, in fact, improvesthe properties as the silicon is increased above 1.5% within this range.A detrimental effect becomes evident at about 3% silicon and becomesquite pronounced when the silicon content exceeds about 3.5%.

It has been found that any free massive carbides existing,yas a` resultof production variables, in the pearlitic castings can be removed by thetreatment above the critical temperature. Magnesium-containing alloyswhich arecarbidic as cast but in which the excess'carbon ispredominantly in the uncombined form and which contain uncombined carbonin `the spheroidal form, such as magnesium-containing alloys which haveVnot been very effectively inoculated, e. g., been held too long in theladle after inoculation, can be heat treated to decompose the freecarbides by means of the high temperature treatment above the criticaltemperature, whereby the amount of uncombined carbon in the form ofspheroidal bodies increases without the development of graphite in flakeform. When the magnesium-containing ferritic product is desired, thistreatment is followed by treatment just below the critical temperature.The production of a ferritized product from such a carbidic casting bythis method will usually require a longer time, particularly in the hightemperature treatment, e. g., at least 2 hours in the high temperaturetreatment and at least 2 hours in the treatment just belowthe criticaltemperature.v

The ferritizing heat treatment provided by the present invention hasbeen found to produce particularly satisfactory results when applied tothe treatment of magnesium-containing castings having av matrixcomprised of pearlite in the as-cast condition. The ferritizing heattreatment can also be applied to other matrices containing combinedcarbon and having the iron in the alpha form at atmospherictemperatures, for example, matrices containing martensite, bainite, etc.However, these nonpearlitic matrices are more diicult to treat and ingeneral require longer treating times to ferritize the matrix, e. g., atleast about 3 or 4 hours. Castings having such anonpearlitic matrix willusually contain larger amounts of alloying elements than Will be presentin a pearlitic casting of an analogous composition. Thus, the presenceof about 4% or more of nickel, e. g., 4.7% nickel, will usually resultin a casting having a martensitic matrix and having a lower criticaltemperature than if made of a similar pearlitic composition containingless nickel.

It will be appreciated from the foregoing that carbides in the as-caststructure of the casting can be decomposed at a temperature at least ashigh'as about 75 F. below the critical temperature, e. g., over a rangeextending from the aforementioned temperature slightly below thecritical temperature up to about 1800 F. When the carbides are massiveprimary carbides, the temperature employed to decompose the carbidesshould exceed the critical temperature, and when the carbides are acomponent of the matrix, the temperature should be within 75 F. belowthe critical temperature.

State of carbon form of carbon having the radiating structure with apolycrystalline appearance has not been conclusively established, but inall tests conducted thereon, the spheroidal form of carbon has exhibitedthe same behavior, color and individual properties as graphite. Thus,the spheroidal form of carbon has a gray color the same as or veryclosely similar to that possessed by graphite. Itis also soft likegraphite. It behaves in the same manner as graphite under chemicaltests. Thus, in the chemical analysis of the alloy provided by theinvention for uncombined carbon, it is obtained as a residue aftertreatf ment with acids in the same manner as a graphite residue isobtained in the chemical analysis of gray cast iron and in the sameproportion to the total carbon as if the spheroidal form of carbon weregraphite. Like graphite, the spheroidal form ofV gray-colored carbonbehaves anisotropically under polarized, reected light. It has a' greasyfeel similar to that exhibited by graphite. No evidence has been foundto indicate that the spheroidal form of carbon is not graphite. Indescribing the present` invention, the carbon in the spheroidal form hasbeen referred to as uncombined carbon in View of its-close resemblancein behavior, color and properties to the uncombined carbon obtained as aresidue after treatment with acids, as in the chemical analysis of graylcast iron-,5 and in'v view of the fact that, like the graphite residue,it

is combustible to a gaseous'compound of carbon 'and oxygen. The termuncombined carbon is employed lixr the conventional metallurgical senseas applied to ferrous alloys such as gray cast iron and refers to thepresence of the carbon in a substantially uncombincd condition. Thus,while the flake graphite of gray cast iron is conventionally referred toas uncombincd carbon, it is known that this flake graphite oftencontains small amounts of other elements, particularly iron.

M echa/:ism of invention While the mechanism involved in the presentinvention is not fully understood theoretically, the conditions whichneed to be met in the production of the as-cast product containing thespheroidal form of uncombincd carbon are believed to comprise (l)establishing a molten ferrous composition which strongly tends to freezeas a white cast iron, yet the carbides of which are at the same timerelatively unstable; and 2) providing a graphitizing tendency opposingthe whitening tendency of the molten composition, such as by providinghigh graphitizing power in the primitive melt or by effectiveinoculation whereby uncombincd carbon is stimulated to startcrystallizing from the melt at a temperature sufficiently high to allowits free growth as spheroids or spheres, largely in liquid surroundings.ing tendencies may be approached variously, provided sufficient controlis exercised. The metallurgical relations of magnesium to iron,including the power it possesses to whiten iron and its limitedsolubility in molten iron, provide a very practical means for thedependable accomplishment of this balance.

As described hereinbefore, the foregoing relationship between opposingtendencies can be realized in accordance with the present invention bymelting a charge to establish a bath or melt of such composition,particularly carbon and silicon content, that if then cast, for example,in sand, would result in gray cast iron which contains ake graphite;adding thereto an agent having a strong whitening effect in cast iron inan amount to produce a whitening effect such that the melt if then castwould freeze as a white cast iron, yet the carbides of which arerelatively unstable; graphitizing the bath or melt, for example, byadding a graphitizer to produce a graphitized bath or melt which whenthen cast into molds of the materials usually employed in casting castiron, e. g., sand, etc., results in a casting of gray cast ironcomposition containing substantial amounts of uncombincd or free carbonin the spheroidal form and preferably substantially devoid of Hakegraphite.

As noted hereinbefore, the metallurgical relations of magnesium to ironmake magnesium the most preferable and a very practical means for thepurpose of carrying out the process described herein. Magnesium has therequired strong whitening effect in cast iron, and when incorporated ina molten gray cast iron in the required amounts results in a bath ormelt which would freeze as a white cast iron, a term which hereinincludes mottled to all-white irons in which the white ironcharacteristics and structural features predominate, yet the carbides ofwhich are at the same time relatively unstable or, in other words, aremetastable carbides. The process disclosed herein thus uses an agenthaving a carbide metastabilizing effect to produce a metastabilizedmelt, i. e., uses a carbide metastabilizing or carbide metastabilizeragent. ln order to oppose the foregoing whitening effect which wouldproduce relatively unstable or metastable carbides, a stronggraphitizing agent, for example, a ferrosilicon inoculant, is added tothe bath or melt to insure that a substantial amount of uncombincdcarbon will be in castings made from the bath or melt upon cooling frompouring temperatures. The graphitized bath or melt is then cast toproduce castings of gray cast iron composition containing uncombincdcarbon or graphite in the desired spheroidal form described andillustrated herein, which form is sometimes also referred to by thoseskilled in the art as This delicate relationship betweenopposspherulitic, spheruliticnodular, nodular and spherulitio, etc.(see, for example, the article by H. Morrogh entitled Nodular GraphiteStructures Produced in Gray Cast Irons published in American Foundryman,April i948, at pages 9l-l06, particularly pages 91 and 92). lt has beenpointed out herein that the agent utilized to provide the requiredwhitening (or carbide metastabilizing) elfect must also stimulate orinduce the carbon, dissolved and dispersed in the bath or melt, tocrystallize as the spheroidal form of uncombincd carbon; in other words,the agent must be of the type sometimes referred to as the spheruliticnodular-impelling type." As previously noted, the iron castings made inaccordance with the present invention are preferably substantiallydevoid of flake graphite, i. e., substantially devoid of the type ofgraphite commonly found in gray cast iron which has sometimes beenreferred to as saucer-shaped or saucer-form flake graphite (see, forexample, the American Society for Testing Materials (A. S. T. M.)Designation A247-41T, issued in 1941 and published, e. g., at page 300in 1941 Supplement to A. S. T. M. Standards, Part I, Metals, November1941).

Applications The present invention may be applied to the manufacture ofa wide variety of ferrous products and articles which will be apparentto those skilled in the art from the properties and structure of theferrous alloy provided by the invention. These products and articlesinclude those made heretofore of ferrous alloys such as gray cast iron,pearlitic malleable iron, ferritic or standard malleable iron, and evencertain grades of cast steels. Illustrative examples of such productsand articles include engine crank shafts, dies, car wheels, beds formachine tools, understructures of large steel mill and railroad weighingscales, machinery parts such as roll mill housings and run-out tablesfor steel mill equipment, rolls such as paper machinery rolls and steelmill rolls, gyratory crusher housings and shells, castings for railroadequipment, for ships, for agricultural implements and machinery and forearth-moving and conveying machinery, pressure castings for valves andpumps such as are used in power stations, in the oil industry and in themining industry, furnace parts, melting and heat treating pots,manifolds and other articles subjected to heat, composite products inwhich the material provided by the invention forms one or morecomponents, e. g., steel mill rolls with machinable necks in combinationwith a non-machinable martensitic body, car wheels having a steel rimwith the material provided by the invention forming the hub and web,composite rolls having roll shells made of the material provided by theinvention, and centrifugally cast products having one metallic materialin the outer portion and another metallic material in the inner portion.innumerable other applications utilizing the improved combination ofproperties provided by the product embodying the present invention willbe apparent to those skilled in the art.

It is to be observed that the present invention provides a novel methodfor producing a novel gray cast iron product having a novel, unusual,and highly useful combination of founding properties and mechanical andphysical properties, and that the novel process provided by theinvention is applicable to cast iron compositions readily handled in thegray cast iron foundry. Thus, in carrying out the present process underpractical foundry conditions in a conventional foundry, ordinary graycast iron baths containing about 3.3% to about 3.6% carbon and about1.7% to about 2% silicon are treated with magnesium and are inoculatedto yield final gray cast iron compositions containing the aforesaidamounts of carbon, about 0.06% to about 0.1% magnesium and about 2.2% toabout 2.7% silicon. The aforesaid baths of ordinary foundry irons arereadily and economically handled in the usual foundry equipment, haveexcellent fluidity and castability, have low shrinkage in the mold,require little 25 feeding, etc., while the aforesaid products have verygood c ombinations of properties.

This application is a continuation-impart of our copending U. S.application Serial No. 787,420, filed November 21, 1947, now Patent No.2,485,760, granted October 25, 1949.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to Without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such variations and modifications apparent to those skilledin the art are considered to be Within the purview and scope of theinvention and the appended claims.

We claim:

1. The method for producing a ductile cast iron having a microstructurecontaining in the as-cast condition uncombined carbon in a spheroidalform and characterized by a high combination of properties whichcomprises establishing a molten ferrous bath containing about 2% toabout 4.5 carbon, about 0.5% to about 3.5% silicon, with the sum of thepercentage of carbon plus one-third the percentage of silicon being notmore than about 5, and the balance a gray cast iron composition whencast in an inoculated condition and having iron in the alpha form atatmospheric temperatures, introducing into said ferrous bath magnesiumin an amount to provide about 0.06% to about 0.15% magnesium in castingsmade from said bath, thereafter inoculating the magnesium-containingbath with about 0.3% to about 2.5 silicon as a silicon-containing agentand casting the metal from said inoculated bath in an inocultedcondition to produce a ferrous alloy casting containing the aforesaidamounts of retained magnesium to cause the occurrence of uncombinedcarbon in a spheroidal form in the as-cast condition and devoid ofsubversive amounts of elements materially interfering with the elfect ofmagnesium in causing the occurrence of uncombined carbon in saidspheroidal form. 2. VThe method for producing a ductile cast iron havinga microstructure containing in the as-cast condition uncombined carbonin a spheroidal form and characterized by a high combination ofproperties which comprises establishing a molten ferrous bath containingabout 2.5% to about 4% carbon, about 0.5% to about 3.5% silicon, withthe sum of the percentage of carbon plus one-third the percentage ofsilicon being not more than about 5, and the balance being a gray castiron composition when cast in an inoculated condition and having iron inthe alpha form at atmospheric temperatures', introducing'into'saidferrous bath magnesium' in an amount to provide about 0.05% to about0.2% magnesium retained in castings made from said bath, thereafterinoculating the magnesium-containing bath with about 0.4% to aboutl 1.2%silicon'as ferrosilicon and casting the metal from said inoculated bathshortly after an inoculation to produce a ferrous alloy castingcontaining the aforesaid amounts of retained magnesium to cause theoccurrence of uncombined carbon ina spheroidal form in the as-castcondition and devoid of subversive amounts of elements materiallyinterfering with the effect of magnesium in promoting the occurrence ofuncombined carbon in said spheroidal form.

3. The method for producing a ductile cast iron having a microstructurecontaining in the as-cast condition uncombined carbon in a spheroidalform and characterized by a high combination of properties whichcomprises establishing a molten ferrous bath containing about 1.7% toabout 4.5% carbon, about 0.8% to about 5% silicon, with the sum of thepercentage of carbon plus one-third the-percentage of silicon being notmore than about 5, and the balance a gray cast iron composition whencast in fan inoculated condition and having iron in the alpha form'y atatmospheric temperatures, introducing into'said ferousbath magnesium inan amount to provide about 0.035% to about 0.4% magnesium retained incastings made from said bath, inoculating the ferrous bath with about0.3% vto about 2.5 silicon as' a silicon-containing agent such that saidinoculation does not precede said magnesium incorporation and castingthe metal from said inoculated bath in an inoculated condition toproduce a ferrous alloy casting containing the aforesaid amounts ofretained magnesium to cause the occurrence of uncombined carbon in aspheroidal form in the as-cast condition and devoid of subversiveamounts of elements materially interfering with the effect of magnesiumin promoting the occurrence of uncombined carbon in said spheroidalform.

4. The method for producing a ductile cast iron having a microstructurecontaining in the as-cast condition uncombined carbon in a spheroidalform and characterized by a high combination of properties whichcomprises establishing a molten ferrous bath having such a compositionas to be a gray cast iron when cast in an inoculated condition andcontaining carbon and silicon such that the sum of the percentage ofcarbon plus one-third the percentage of silicon does not exceed 5,introducing into said ferrous bath magnesium in an amount sucient toprovide at least a small but effective amount up to about 0.5% magnesiumretained in castings made from said bath, inoculating the ferrous bathwith at least about 0.2% silicon as a siliconcontaining agent such thatsaid inoculation does not precede said magnesium incorporation andcasting the metal from said inoculated bath in an inoculated conditionto produce a ferrous alloy casting having iron in the alpha form andcontaining the aforesaid amounts of retained magnesium to cause theoccurrence of uncombined carbon in a spheroidal form in the as-castcondition and devoid of subversive amounts of elements materiallyinterfering with the effect of magnesium in promoting the occurrence ofuncombined carbon in said spheroidal form.

5. The method according to claim 4 wherein magnesium is incorporatedinto the molten ferrous bath in the form of an alloy containing about 4%magnesium with the balance essentially nickel.

6. The method of producing an improved gray cast iron having the freecarbon thereof in spheroidalforrn comprising melting a charge of iron ofsuch carbonand silicon content that if cast in an inoculated conditionwould result in a gray cast iron containing ake graphite, introducingmagnesium into said melt in quantities suicient to produce a white castiron if cast, and thereafter graphitizing the melt suflciently toproduce a spheroidal graphite gray cast iron casting from the melt withsubstantially complete absence of ake graphite.

7. vThe method of producing cast iron comprising melting a chargel ofsuch composition that if inoculated and cast in vsand would result in agray cast iron containing flake graphite, introducing magnesium into themelt in such amount that the treated melt if cast in sand would resultin a white iron, adding a graphitizing agent to the melt in such amountthat the graphitized melt if cast in sand would result in gray iron, andfinally pouring a casting from said melt.

8. The' method of producing graphitic cast iron having the free carbonthereof in nodular and spherulitic form comprising, melting a charge ofiron of such carbon and silicon content that if cast in the absence of acarbidemetastabilizer agent of the spherulitic nodular-impelliug typewould result in a gray cast iron containing saucerform flake graphite,and adding said carbide-metastabilizer agent to the melt in quantitysucient to produce a mottled to-all-white iron if cast, themetastabilizer agent dissolving and dispersing the carbon in the melt,andi thereafter graphitizing the melt sufdciently to produce aspherulitic modular-graphite gray cast iron casting from the melt withsubstantially complete absenceof saucerform flake graphite. v.

9. The method of producing cast iron comprising, melting a charge ofsuch composition that if cast in sand would result in a gray cast ironcontaining flake graphite,v adding a carbide-metastabilizingagent tothemelt in 27 such amount that the treated melt if cast in sand wouldresult in a substantially mottled to all-white iron, adding agraphitizing agent to the meta-stabilized melt in such amount that thegraphitized melt if cast in sand would result in gray iron, and nallypouring a casting from said melt.

l0. The method of producing graphitic cast iron having the free carbonthereof in nodular and spherulitic form comprising, melting a charge ofiron of such carbon and silicon content that if cast in the absence of acarbidemetastabilizer agent of the spherulitic nodular-impelling typewould result in a gray cast iron containing saucerform flake graphite,and adding said carbide-metastabilizer Iagent to the melt in quantitysufficient to produce a mottled to all-white iron if cast, andthereafter graphitizing the melt sufficiently to produce a spheruliticnodulargraphite gray cast iron casting from the melt with substantiallycomplete absence of saucer-form ake graphite.

l1. The method of producing graphitic cast iron having uncombined carbonin spheroidal form as cast comprising establishing a molten ironcomposition of such carbon and silicon content that if cast in aninoculated condition it would result in a gray cast iron containingflake graphite, introducing in said molten iron compositionmagnesium inan amount less than about 0.5% but sufficient to produce a cast ironwhich tends, if cast, to be white cast iron containing relativelyunstable carbides and graphitizing the molten iron composition, andcasting molten magnesium-containing iron to produce a spheroidalgraphite cast iron.

12. A method of producing an improved graphitic cast iron having amicrostructure containing uncombined carbon in the as-cast condition inspheroidal form in a matrix having iron in the alpha form whichcomprises establishing a melt of molten iron composition containing atleast about 87% iron and an amount of magnesium sufficient in theabsence of inoculation to cause the molten iron composition to possesshigher chilling propensity than the molten iron composition Withoutmagnesium, said melt being one which in the absence of magnesium wouldproduce, when cast, gray cast iron having its uncombined carbonpredominantly in the form of ake graphite; inoculatingmagnesium-containing iron from said melt with a graphitizing agent; andcasting the inoculated magnesium-containing iron to obtain a graphiticcast iron containing at least about 87% iron and containing in theascast condition uncombined carbon in a spheroidal form in a matrixhaving iron in the alpha form.

13. A method of producing an improved graphitic cast iron having amicrostructure containing uncombined carbon in the as-cast condition insubstantially spheroidal form in a matr-ix having iron in the alpha formcomprising establishing a molten iron composition which if cast in aninoculated condition would be a gray cast iron containing tiake graphitein a matrix having iron in the alpha form, introducing in said molteniron composition an amount of magnesium suiiicient to cause the molteniron composition to tend to freeze as a white cast iron containingcarbides which are relatively unstable, introducing an inoculant in themolten iron composition to provide a graphitizing effect to overcome thewhitening tendency of the molten magnesium-containing iron composition,and casting the molten magnesium-containing iron composition in aninoculated condition and with less than about 0.02% sulfur to obtain agraphitic cast iron having iron in the alpha form and beingsubstantially devoid of subversive amounts of elements materiallyinterfering with the effect of magnesium in promoting the occurrence ofuncombined carbon in a substantially spheroidal form in the graphiticcast iron in the as-cast condition.

14. A method of producing an improved graphitic cast iron having amicrostructure containing uncombined carbon in the as-cast condition inspheroidal form in a matrix having iron in the alpha form whichcomprises introducing in a molten iron bath of such composition that, if

cast in an inoculated condition, it would be a gray cast iron havingiron in the alpha form and containing ake graphite, an amount ofmagnesium suicient to provide a molten composition which strongly tendsto freeze as a white cast iron containing carbides which are relativelyunstable and containing less than about 0.02% sulfur, introducing agraphitizer in the molten iron composition to provide a graphitizingtendency overcoming the whitening tendency imparted by the magnesium tothe molten iron composition, and casting the treated molten ironcomposition to obtain a graphitic cast iron having iron in the alphaform and substantially devoid of subversive amounts of elementsmaterially interfering with the aforesaid occurrence of spheroidaluncombined carbon when cast.

l5. A method of producing a casting of an improved graphitic cast ironhaving a microstructure containing uncombined carbon in the as-castcondition in spheroidal form in a matrix having iron in the alpha formwhich comprises establishing a molten iron composition which, if cast inan inoculated condition, would be a gray cast iron containing at leastabout 87% iron and containing flake graphite in a matrix having iron inthe alpha form, introducing in said molten iron composition magnesium inan amount less than about 0.2% suflicient in the absence of inoculationto cause the molten iron composition to tend to freeze as a white castiron containing carbides which are relatively unstable and introducing asiliconcontaining inoculant to provide a graphitizing effect, andthereafter casting in an inoculated condition moltenmagnesium-containing iron with less than about 0.02% sulfur andsubstantially devoid of subversive amounts of elements materiallyinterfering with the effect of magnesium in promoting the occurrence ofspheroidal uncombined carbon into a casting of graphitic cast ironcontaining at least about 87% iron and having a microstructurecontaining uncombined carbon in the as-cast condition in spheroidal formin a matrix containing iron in the alpha form.

16. The method of making an improved graphitic cast iron which comprisesproducing a molten iron composition having such carbon and siliconcontent and such graphitizing power that if cast it would produce graycast iron containing flake graphite in a matrix having iron in the alphaform; treating said molten iron composition to introduce thereinmagnesium in the presence of high graphitizing power and in an amountsuicient to induce the occurrence of uncombined carbon in asubstantially spheroidal form in the graphitic cast iron when cast; andthereafter casting the molten iron composition, while retained magnesiumand graphitizing power are effective, to produce graphitic cast ironpossessing, when cast, a microstructure containing uncombined carbon ina substantially spheroidal form in a matrix containing iron in the alphaform.

17. A method as set forth in claim 16 wherein a graphitizing inoculantis added to provide high graphitizing power.

18. In a method for producing graphitic cast iron, the improvementcomprising establishing a molten iron composition having a cast ironcomposition containing at least about 87% iron, introducing magnesium insaid molten iron composition in suicient amount to provide in the castiron when cast a retained magnesium content less than about 0.5% andsuicient to promote the occurrence of substantially spheroidal graphitein the graphitic cast iron when cast and adding a graphitizing inoculantto said molten iron composition in such manner that it does notsubstantially precede the magnesium introduction and in an amountadequate to produce graphitic cast iron when cast, whereby a casting ofmagnesium-containing graphitic cast iron can be produced having astructure in the as-cast condition containing graphite in asubstantially spheroidal form.

19. A method of producing an improved graphitic cast iron having amicrostructure containing uncombined carbon in the as-cast condition insubstantially spheroidal form in a matrix having iron in the alpha formwhich comprises establishing a molten iron composition which, in theabsence of magnesium, would produce gray cast iron having its uncombinedcarbon substantially in the form of flake graphite and which contains atleast about 87% iron and magnesium less than about 0.5% effective toinduce, when cast after inoculation, the occurrence of uncombined carbonin a substantially spheroidal form; subsequently inoculating said molteniron composition containing magnesium with a graphitizing agent; andcasting said inoculated magnesium-containing iron composition to obtaina graphitic cast iron containing at least about 87% iron and containingin the `as-cast condition uncombined carbon in a substantiallyspheroidal form in a matrix having iron in the alpha form.

20. The method of producing an improved graphitic cast iron having amicrostructure containing when cast uncombined carbon in a substantiallyspheroidal form which comprises establishing a molten iron compositionwhich lif cast in an inoculated condition would be a gray cast ironcontaining ake graphite, introducing into said molten iron compositionan amount of magnesium suilicient to retain less than about 0.5magnesium therein effective to induce the occurrence of at least about25% of the uncombined carbon in a substantially spheroidal form whencast and inoculating the molten iron composition with asilicon-containing graphitizer, and thereafter casting the inoculatedmagnesium-containing iron to obtain a graphitic cast iron having atleast about 25% of the uncombined carbon therein in a substantiallyspheroidal form in the as-cast condition.

2l. A method for producing an improved graphitic cast iron having astructure in the as-cast condition containing uncombined carbon insubstantially spheroidal form comprising establishing a molten ironcomposition which would be gray cast iron containing flake graphite ifcast in an inoculated condition, introducing magnesium into said molteniron composition in suicient amount to provide in the graphitic castiron when cast a retained magnesium content suiiicient to promote theoccurrence of at least about 25% of the graphite in substantiallyspheroidal form in said graphitic cast iron when cast, adding agraphitizing inoculent to said molten iron composition in such mannerthat it does not substantially precede the magnesium introduction and inan amount suiicient to produce graphitic cast iron when cast, andthereafter casting said magnesiumcontaining, inoculated molten iron toobtain graphitic cast iron containing at least about 25% of the graphitein substantially spheroidal form.

22. A method for producing improved graphitic cast iron comprisingestablishing a molten iron bath having such a cast iron compositionthat, if cast after inoculation, it would have a gray cast ironstructure and would contain about 1.7% to about 5% carbon, about 0.5% toabout 6% silicon, and at least 87% iron; introducing magnesium in themolten iron composition in suiicient amount to provide in the graphiticcast iron when cast a retained magnesium content less than about 0.5sufficient to promote the occurrence of substantially spheroidalgraphite in said graphitic cast iron and providing a graphitizinginoculant in an amount adequate to produce graphitic cast iron, whencast; and thereafter casting the molten magnesium-containing ironcomposition in an inoculated condition and with low sulfur and oxygen toobtain a graphitic cast iron containing at least about 87% iron, havingiron in the alpha form and containing uncombined carbon in asubstantially spheroidal form in the as-cast condition.

23. The method of producing an improved graphitic cast iron having amicrostructure containing when cast at least about 25% of the uncombinedcarbon in a substantially spheroidal form in a matrix having iron in thealpha form which comprises establishing a molten iron bath having such acomposition that if cast in an inoculated condition it would be a graycast iron containing at least about 87% iron and containing ake graphitein a matrix having iron in the alpha form, introducing into the molteniron composition an amount of magnesium sufcient to retain less thanabout 0.2% magnesium'therein effective to induce the occurrence of atleast about 25 of the uncombined carbon in a substantially spheroidalform and inoculating the molten iron composition with asilicon-containing graphitizer, and casting inoculatedmagnesium-containing molten iron with a sulfur content less than about0.02% to obtain a graphitic cast iron containing at least about 87% ironand having at least about 25% of the as-cast uncombined carbon thereinin a substantially spheroidal form in a matrix having iron in the alphaform.

References Cited in the le of this patent UNITED STATES PATENTS1,801,742 Hayes Apr. 21, 1931 2,467,406 Reece Apr. 19, 1949 2,485,760Millis et al. Oct. 25, 1949 2,496,863 Deschamps et al Feb. 7, 1950 OTHERREFERENCES Cast Metals Handbook, 1944 edition, pages 523 to 526.

1. THE METHOD FOR PRODUCING A DUCTILE CAST IRON HAVING A MICROSTRUCTURE CONTAINING IN THE AS-CAST CONDITION UNCOMBINED CARBON IN A SPHEROIDAL FORM AND CHARACTERIZED BY A HIGH COMBINATION OF PROPERTIES WHICH COMPRISES ESTABLISHING A MOLTEN FERROUS BATH CONTAINING ABOUT 2% TO ABOUT 4.5% CARBON, ABOUT 0.5% TO ABOUT 3.5% SILICON, WITH THE SUM OF THE PERCENTAGE OF CARBON PLUS ONE-THIRD THE PERCENTAGE OF SILICON BEING NOT MORE THAN ABOUT 5, AND THE BALANCE A GRAY CAST IRON COMPOSITION WHEN CAST IN AN INOCULATED CONDITION AND HAVING IRON IN THE ALPHA FORM AT ATMOSPHERIC TEMPERATURES, INTRODUCING INTO SAID FERROUS BATH MAGNESIUM IN AN AMOUNT TO PROVIDE ABOUT 0.06% TO ABOUT 0.15% MAGNESIUM IN CASTINGS MADE FROM SAID BATH, THEREAFTER INOCULATING THE MAGNESIUM-CONTAINING BATH WITH ABOUT 0.3% TO ABOUT 2.5% SILICON AS A SILICON-CONTAINING AGENT AND CASTING THE METAL FROM SAID INOCULATED BATH IN AN INOCULTED CONDITION TO PRODUCE A FERROUS ALLOY CASTING CONTAINING THE AFORESAID AMOUNTS OF RETAINED MAGNESIUM TO CAUSE THE OCCURRENCE OF UNCOMBINED CARBON IN A SPHEROIDAL FORM IN THE AS-CAST CONDITION AND DEVOID OF SUBVERSIVE AMOUNTS OF ELEMENTS MATERIALLY INTERFERING WITH THE EFFECT OF MAGNESIUM IN CAUSING THE OCCURRENCE OF UNCOMBINED CARBON IN SAID SPHEROIDAL FORM. 